Production of improved lubricating oils

ABSTRACT

Lube oils of improved viscosity index are produced by subjecting a crude lubricating oil to hydrocracking, selectively fractionating the hydrocracked product to yield a product having the desired flash point and viscosity and recycling the fractionator bottoms to the hydrocracking zone.

Ultited States Patent Coleman et al.

PRODUCTION or IMPRovEd warucxrmo OILS Inventors: Richard L. Coleman, Port Arthur;

Billy H. Cummins, Nederland; Ambrose J. Startz, Groves, all of Tex.

Assignee: Texaco, Inc., New York. NY.

Filed: June 15, 1973 Appl. No.: 370,246

U.S. Cl. 208/95; 208/18; 208/96 Int. Cl Cl0g 13/04 Field of Search 208/l8, 111, 112, 95

References Cited UNlTED STATES PATENTS 4/1957 Watkins et a1 208/58 451 July 22, 1975 3,l42,634 7/]964 Ireland et al 208/95 3,l42,635 7/l964 Coonradt et al i 208/l l l 3.242068 3/1966 Peterson i r i 208/] l I 3,285,848 ll/l966 Donaldson et al 208/110 3308,055 3 /l9 67 Kozlowski 208/] ll 3.562,l49 2/197! Bryson et al..... 208/l43 3.660.273 5/1972 Cummins 208/96 Primary Exarii'irir-Hflbmt Levine Attorney. Agent. or FirmT. H. Whaley; C. G. Ries; Robert Knox 9 Claims, No Drawings PRODUCTION OI" IMPROVED LUBRICATING OILS This invention relates to the production of improved petroleum oils. More particularly it is concerned with the production of base oils of high viscosity index suitable for blending into multigrade lubricating oils, automatic transmission fluids and other specialty oils requiring high viscosity index. In one of its more specific aspects, it is concerned with the production of high viscosity index lubricating oils in good yield from lubricating oil charge stocks using a process sequence which includes in a preferred embodiment hydrocracking, selective fractionation and dewaxing.

Various steps for the refining of lubricating oils such as distillation, solvent refining, solvent dewaxing, acid treating and clay contacting are well known. When residual type oils are being processed, a preliminary step of deasphalting is also generally required.

[n the processing steps listed above, distillation is employed as a means of separating a crude oil into fractions of various viscosities, solvent refining with, for example, furfural, sulfur dioxide or N-methyl-2- pyrrolidone is ordinarily used as a means of removing aromatic compounds and thereby improving the viscosity index, solvent dewaxing using for example a mixture of methyl ethyl ketone and toluene is used to improve low temperature properties by lowering the pour point of the oil and clay contacting is used generally as a final step to further improve the color and to neutralize the oil, after it has been acid treated to improve color, oxidation and heat stability.

In a typical operation, a crude oil is topped under atmospheric pressure to produce light distillates such as naphtha, kerosene and atmospheric gas oils and an atmospheric reduced crude which is then vacuum distilled to produce lube oil distillates with the residue from the vacuum distillation being deasphalted to yield residual lubricating stocks. Conventionally, the various lube oil fractions are then further processed by solvent refining and dewaxing. With the advent of mild hydrogenation, acid treating and clay contacting have more or less fallen into disuse.

Because of the increasing demand for the lighter grade lubricating oils it has been found advantageous to convert the heavier oils to the more valuable lighter products by hydrocracking, or severe hydrotreating. Not only does this result in an increase in yield of desired lube oil fractions but because of the high hydrogen pressures involved which result in a reduction in the aromatic content of the oil, hydrocracking and hydrotreating have been proposed as replacements for solvent refining.

Conventionally, when a crude lubricating oil is hydrocracked, the effluent from the hydrocracking zone is passed through a high pressure separator for removal of a hydrogen-rich gas then through a low pressure separator for removal of low molecular weight normally gaseous hydrocarbons. The balance of the effluent is then sent to a fractionator where, to obtain a hydrocracked lube oil having a satisfactory flash point, the material boiling below about 600F. is removed. The 600F+ material is then considered as product. One drawback to this method of operation is that if it is desired to change the product viscosity it is necessary to change the reaction conditions or to use a charge stock from a different source or both. However, a change in the reaction conditions also produces change in the product viscosity index.

it is an object of the present invention to produce lubricating oils of specified flash point and viscosity without changing the hydrocracking reaction conditions or conversely, to change the hydrocracking reaction conditions while continuing to produce a product of constant specifications.

According to our invention a crude petroleum lubricating oil is subjected to hydrocracking to improve its viscosity index, the hydrocraclted product is subjected to selective fractionation, the desired fraction is dewaxed and that portion boiling above the desired fraction is recycled to the hydrocracking zone.

The process of the invention may be applied to a variety of petroleum feedstocks. For example, the feed may be obtained by subjecting a vacuum residuum to deasphalting with a low molecular weight hydrocarbon such as propane or butane. The deasphalted residuum can then be hydrocracked. It is also possible to use a wax distillate as feed to the hydrocracking stage. The feed whether obtained by distillation or by deasphalting a vacuum residuum may be subjected to hydrocracking. It is also possible to use as the feed a lubricating oil fraction which has been obtained from a residuum such as an atmospheric residuum or vacuum residuum by a simultaneous deasphalting-solvent refining procedure in which the residuum is treated not with the conventional low molecular weight hydrocarbon deasphalting agents but with a solvent such as furfural or N-methyl- 2-pyrrolidone and the raffinate of reduced aromatic and asphalt content is charged to the hydrocracking zone.

The reaction conditions for the hydrocracking may be varied depending on the product desired and on the charge stock. Typical reaction conditions include a temperature of about 700-900F., preferably 750-850F. The hydrogen partial pressure may range between about 500 and 5000 psig. a preferred range being from 1500 to 3000 psig. Space velocities may vary between about 0.1 and 3.0 v/v/hr. with a preferred range being 0.2-1.0 Hydrogen rates of from l000l0,000 SCFB have been found satisfactory al though rates of 3000-7000 SCFB are preferred.

Hydrogen from any suitable source such as electrolytic hydrogen, hydrogen obtained from the partial combustion of hydrocarbonaceous material followed by shift conversion and purification or catalytic reformer by-product hydrogen may be used. The hydrogen should have a purity of between about 50 and 100% with hydrogen purities of at least 65 volume being preferred, a particularly preferred range being -95% purity.

The oil and hydrogen ordinarily are preheated and brought into contact with a particulate catalyst. The catalyst may be in the form of a fixed bed, a moving bed, a fluidized bed or may be slurried with the oil. In the case of a fixed bed, hydrogen flow may be upward or downward through the reactor as may be the flow of the oil. In a specific embodiment, both the oil and a portion of the hydrogen are introduced at the top of a reactor containing a fixed bed of the catalyst, the balance of the hydrogen being introduced at intermediate points in the reactor for cooling purposes.

The catalyst for the hydrocracking step preferably comprises as a hydrogenating component a compound of a Group VI metal such as molybdenum, chromium or tungsten or a compound of a Group VIII metal such as cobalt, iron or nickel and mixtures thereof. Ordinarily the catalyst is charged to the reactor in oxide form although it can be expected that some reduction and some sulfidation take place during the course of the process so that after being on stream for some time, the catalyst is probably a mixture of the metal, the metal sulfide and perhaps the oxide. If desired, the catalyst after being charged to the reactor but prior to the institution of the on-stream period may be converted at least in part to the sulfide form for example by contact with a gas such as a mixture of hydrogen and sulfiding agent, e.g. hydrogen sulfide, methyl mercaptan or carbon disulfide at an elevated temperature, eg 400F. The group VIII metal may be present in an amount varying from I to 20% by weight of the total catalyst composite, preferably 2-l5% and the group VI metal may be present in an amount ranging from about 540%, preferably 7-25%. Preferred combinations are nickel-tungsten, nickel-molybdenum and cobaltmolybdenum.

The hydrogenating component is supported on a refractory inorganic oxide such as hydrogen form or decationized zeolite Y, alumina, zirconia, silica or magnesia and mixtures thereof optionally promoted with an acidic material such as boron oxide or a halogen.

' Advantageously, the catalyst has a surface area of at least 150 m lg, a pore volume of at least 0.5 cc/g a major portion of the pore volume being made up of pores having an average pore diameter between 50 and I A. The upper limit of the surface area and pore volume is governed. by the hardness and ruggedness of the catalyst. As a practical matter, for commercial installations where the catalyst is used in units capable of processing several thousand barrels of charge per day, the surface area probably should not exceed about 600 mlg and the pore volume should not exceed about 0.8 cc/g.

The catalyst which may be in the shape of pellets, extrudates or spheres, may be prepared by any of the methods well known in the art, such as by impregnating the support with a solution of a salt of one of the metals, filtering, drying and then if desired impregnating with a solution of a salt of another metal, filtering, drying and calcining in a manner well known in the art.

7 The effluent from the hydrocracking zone is cooled and, in one embodiment of the invention, hydrogenrich gas is separated therefrom and recylced to the hydrocracking zone. Optionally, the hydrogen-rich stream is treated to remove any hydrogen sulfide and ammonia contained therein or a portion thereof may be bled from the system to prevent the build-up of hydrogen sulfide, ammonia and/or low molecular weight hydrocarbons. Hydrogen is added to the recycle stream to replace that consumed by the hydrocracking and if necessary to replace any hydrogen purged from the system. The balance of the hydrocracking zone effluent then is passed to a low pressure separator for the removal of low molecular weight hydrocarbons and then to a fractionator for removal of hydrocarbons boiling below about 600F. The 600F+ material may be sent to a second fractionator to obtain a lube oil fraction of the desired flash point and viscosity or the low pressure separator bottoms may be fractionated to produce suitable flash point and viscosity material in the initial frac' tionator. The desired flash point is obtained by removing the light ends and an oil of the desired viscosity may be removed from the fractionator as a side stream or heart cut. The high viscosity bottoms may then be returned to the hydrocracking zone.

By following the procedure outlined above, the deficiencies of the prior art are overcome. In conventional processing, if it were desired to adjust a lube oil hydrocracking process to produce a product oil of higher viscosity the severity of the hydrocracking reaction conditions would be reduced resulting in the higher viscosity product but the product viscosity index would be lower. However, by the procedure of our invention it is possible to produce higher viscosity lube oils without sustaining any loss in the viscosity index of the product.

Advantageously, if it is desired to produce a lube oil having stability to ultraviolet light, the oil should be subjected to a solvent extraction treatment using a selective solvent such 'as furfural or N-methyl-Z- pyrrolidone in any conventional liquid-liquid contacting apparatus such as a packed'column, a centrifugal contactor, a rotating disc contactor or the like. The solvent extraction is carried out at any stage of the process after the hydrocracking, preferably immediately prior to dewaxing.

The following examples are submitted for comparative and illustrative purposes only.

EXAMPLE I In this example, which is representative of conventional processing, the charge is a deasphalted residuum l-Iydrocracking of the charge oil is effected by passing it downwardly with hydrogen through a bed of catalyst pellets containing 2.3 wt. cobalt, I03 wt. molybdenum, 3.9 wt. silica and 79.7 wt. alumina having a pore volume of 0.63 cc/g and a surface area of 290 m /g at a temperature of 805F., a pressure of 1500 psig, 5000 SCFB of purity hydrogen at an hourly space velocity of 0.5 volumes of charge oil per volume of catalyst per hour. The 600F.+ portion of the prodnot, obtained in 63.8 volume per cent basis charge to the hydrocracker has the following characteristics:

This example follows the procedure of our invention in which a high viscosity oil having substantially the same flash point as that obtained in Example I is produced without incurring a loss in viscosity index. The flow differs from that of Example I in that the charge includes a recycle fraction obtained by fractionating the hydrocracked product to produce a heart cut having a suitable flash point and the desired (pre-dewaxed) viscosity. This is accomplished by topping the 600F.+ hydrocracked fraction to obtain an oil of suitable flash point and cutting out an intermediate fraction which,

when dewaxed will have the desired viscosity leaving 5 still bottoms which are recycled and introduced with fresh feed to the hydrocracking zone. The fractionator is operated at an average vacuum of 29.2 inches of mercury and a maximum temperature of 680F. The charge, including recycle, has the following characteristics:

TABLE 3 Gravity, IAPI 23.2 Viscosity, sus, IF. 3034 2l0F. l64.0 Viscosity index 92 Hydrocraclting conditions, using the same catalyst as in Example I, are a temperature of 8l9F., a pressure of 1500 psig a space velocity of 0.5 v/v/hr. and a hydrogen rate of 5000 SCFB. The 600F.+ portion of the product, obtained in a yield of 72.4 vol. has the following characteristics:

TABLE 4 Gravity, API 3L2 Viscosity, SUS, IOOF. 162.7 2IO'F. 46.5 Viscosity index 14] TABLE 5 heart out dewaxed Gravity. APl 31.7 28.1 Viscosity, SUS, 100F. B2 149 ZIO'F 43.1 43.8 Viscosity Index 12 I 13 Flash point, P. 375F.

Pour point, F. +3

By way of comparison, by the procedure of Example I, a dewaxed oil having a viscosity SUS at 100F. of I49 would have a viscosity index of less than 108.

Obviously, various modifications of the invention as hereinbefore set forth may be made without departing from the spirit and scope thereof, and therefore, only such limitations should be made as are indicated in the appended claims.

We claim:

1. A process for the production of a lubricating oil of specified flash point and viscosity which comprises subl5 jecting a crude lubricating oil to catalytic hydrocraclting, distilling the hydrocraclced product to remove material boiling up to about 600F., subjecting the hydrocracked fraction boiling above about 600F. to additional distillation to obtain a lubricating oil having a predetermined flash point, distilling said lubricating oil of predetermined flash point until a heart out is obtained having substantially the same viscosity as said fraction boiling above about 600F., returning the remainder of the hydrocracked fraction boiling above said heart cut to the hydrocracking zone and dewaxing said heart cut.

2. The process of claim 1 in which the heart out is subjected to solvent extraction for the removal of aromatic hydrocarbons prior to being dewaxed.

3. The process of claim 1 in which the crude lubricating oil is a wax distillate.

4. The process of claim 1 in which the crude lubricating oil is a deasphalted residuum.

5. The process of claim 1 in which the hydrocracking catalyst comprises a Group Vlll metal or compound thereof supported on an amorphous inorganic oxide having a surface area of at least 250 mlg and a pore volume of at least 0.5 cc/g.

6. The process of claim 5 in which the amorphous inorganic oxide comprises a mixture of silica and alumina.

7. The process of claim 6 in which the mixture of amorphous inorganic oxide comprises between 2 and 15 wt. silica.

8. The process of claim 2 in which the solvent is furfural.

9. The process of claim 2 in which the solvent is N-methyl-Z-pyrrolidone. 

1. A PROCESS FOR THE PRODUCTION OF A LUBRICATING OIL OF SPECIFIED LASH POINT AND VISCOSITY WHICH COMPRISES SUBJECTING A CRUDE LUBRICATING OIL TO CATALYTIC HYDROCRACKING, DISTILLING THE HYDROCRACKED PRODUCT TO REMOVE MATERIAL BOILING UP TO ABOUT 600*F. SUBSJECTING THE HYDROCRACKED FRACTION BOILING UP TO ABOUT ABOUT 600*F. TO ADDITIONAL DISTILLATION TO OBTAIN A LUBRICATING OIL HAVING A PREDETERMINED FLASH POINT, DISTILLING SAID LUBRICATING OIL OF PREDETERMINED FLASH POINT UNTIL A HEART CUT IS OBTAINED HAVING SUBSTANTIALLY THE SAME VISCOSITY AS SAID FRACTION BOILING ABOVE ABOUT 600*F., RETURNING THE REMAINDER OF THE DROCRACKED FRACTION BOILING ABOVE SAID HEART CUT TO THE HYDROCRACKING ZONE AND DEWAXING SAID HEART CUT.
 2. The process of claim 1 in which the heart cut is subjected to solvent extraction for the removal of aromatic hydrocarbons prior to being dewaxed.
 3. The process of claim 1 in which the crude lubricating oil is a wax distillate.
 4. The process of claim 1 in which the crude lubricating oil is a deasphalted residuum.
 5. The process of claim 1 in which the hydrocracking catalyst comprises a Group VIII metal or compound thereof supported on an amorphous inorganic oxide having a surface area of at least 250 m2/g and a pore volume of at least 0.5 cc/g.
 6. The process of claim 5 in which the amorphous inorganic oxide comprises a mixture of silica and alumina.
 7. The process of claim 6 in which the mixture of amorphous inorganic oxide comprises between 2 and 15 wt. % silica.
 8. The process of claim 2 in which the solvent is furfural.
 9. The process of claim 2 in which the solvent is N-methyl-2-pyrrolidone. 